Polymerization of alpha-olefins, such as ethylene, propylene and butene-1, to normally-solid, substantially crystalline polymers using catalyst compositions comprising transition metal and organoaluminum compounds is well known. Although many transition metal compounds have been disclosed as useful in such polymerizations, including salts of titanium, vanadium and zirconium, compounds of titanium predominate with tetravalent titanium (Ti(IV)) compounds typically proving most useful in ethylene polymerization and trivalent titanium (Ti(III)) compounds most useful in polymerization of propylene and higher alpha-olefins. Various forms of titanium components have been disclosed in both Ti(IV)- and Ti(III)-based compositions including a so-called "supported" titanium component. Supported titanium catalyst components have been disclosed in which titanium (either Ti(III) or Ti(IV)) is placed onto a metal oxide or metal halide support. One view of an advantage of supported titanium catalyst components is that in such components catalytically active titanium-containing sites are dispersed throughout the supported catalyst composition yielding more efficient use of the titanium content and resulting in higher overall catalytic activity, especially if based on titanium content.
Supported titanium catalyst components have been found most useful in ethylene polymerization such as described in U.S. Pat. No. 3,901,863. Until recently, however, supported titanium catalyst components have not been used substantially in commercial polymerization of propylene or higher alpha-olefins due to coproduction of high levels of noncrystalline or amorphous polymeric products. Production of such noncrystalline, amorphous products especially is detrimental in polymerization processes in which such noncrystalline products are not removed by solvent extraction.
Examples of nonsolvent processes are gas-phase and bulk processes. In gas-phase polymerization, solid polymer is formed directly on contact of gaseous monomer with a catalyst; while in a bulk process, polymer is formed in a liquid monomer medium. In either process solid polymer advantageously is not treated further with a hydrocarbon solvent to remove noncrystalline material. Even in a slurry process in which noncrystalline material can be removed, production of such noncrystalline material usually is minimized because of its lower economic value.
Supported olefin polymerization catalysts have been disclosed in which crystallinity-promoting components are incorporated. Such components can be electron donor compounds which are associated with titanium-containing supported catalyst complexes. Further, preparations of supported olefin polymerization catalysts have been disclosed in which the supported catalyst material is comminuted such as by ball-milling in order to increase catalyst activity. An example of such catalyst material is described in U.S. Pat. No. 4,277,370 incorporated by reference herein. However, it has been found that while comminuting such a catalyst component can increase activity, presumably by exposing more active sites, such a comminuted catalyst also can yield increased noncrystalline polymer products as evidenced by increased solubles and extractables.
Olefin polymerization catalysts having higher activity and yielding fewer undesirable by-products are always desirable. Many supported titanium-containing catalyst components which have been comminuted such as by ball-milling have been found to be active; however, such a comminuted supported catalyst component which also yields low amounts of noncrystalline polymeric by-products would be very desirable. A method to produce such a catalyst would be very useful in the olefin polymerization catalyst art.
An important commercial property of olefin polymers such as polypropylene is the morphology of powder product. Morphology is a term describing a combination of physical properties of a batch of polymer particles including average pore diameter, absence of very small particles ("fines") or large particles, and substantial uniformity of particles. One measurement used in evaluating morphology is bulk density. Typically, higher bulk density values are desired such as above about 22 pounds per cubic foot or higher. A catalyst which is active, and yields low amounts of amorphous products and a high bulk density powder would be very desirable.